This invention generally relates to accessories for ladders that improve the traction between the upper portion of the ladder and a supporting surface, and more specifically, to an attachment for a ladder that enables the ladder to be more securely positioned against either a round or a flat surface.
Death and serious injury frequently are the result of accidents involving ladders, both in the home and in the workplace. Numerous regulations and safety practices have been promulgated by government agencies, such as the Occupational Safety and Health Administration (OSHA) and the National Institute of Occupational Safety and Health (NIOSH), to prevent such injuries. Ladders are commonly available in two categories, including those that are self-supporting and those that are not. Self supporting ladders, which include certain specialty ladders, three-point ladders, and step-ladders, are typically available in shorter lengths, are generally more expensive, and tend to be heavier. Non-self-supporting ladders, such as one-piece straight ladders, and extension ladders, are quite common and used extensively.
For convenience, the term xe2x80x9cladderxe2x80x9d as used hereafter in this discussion, and in the specification and claims that follow, shall refer only to non-self-supporting ladders, as opposed to self-supporting ladders.
Ladders are generally leaned against a tree, a pole, a building, a wall, or other structure when in use. Care must be taken to ensure that both the base and the top of the ladder are secured to prevent slippage. A variety of safety accessories are readily available to help secure the base of the ladder, preventing it from shifting. Hooks and other attachments are also available that improve the grip of the top of the ladder on a surface to prevent the top of the ladder from shifting laterally. Preventing the top of the ladder from shifting has proved particularly difficult when the structure that the ladder is being leaned against is round or irregular in shape. When the top of the ladder engages a planar surface, a reasonably secure contact can normally be obtained. However, when the surface is round, like a pole or a tree, it is difficult to prevent the ladder from rotating around the point of contact of the top rung against the round surface, since the stiles of the ladder are usually not positively supported. With the upper rung of the ladder rather than the stiles of the ladder resting against the supporting surface, the ladder will generally feel precarious and be prone to shifting.
The prior art has developed devices to enable a more positive engagement between the upper portion of a ladder and a non-planar or generally cylindrical surface. U.S. Pat. No. 4,469,194 (McBride) discloses a sponge-like block having a semicircular metal member that engages the top rung of a ladder, so that the sponge-like block stabilizes the ladder when the ladder is rested against a wall, tree, or pole. The semicircular metal member is secured to the sponge rubber block using adhesive or rivets. The ends of the semicircular member, which extend beyond each end of the block, are attached to the top rung of the ladder using clamps (such as common hose clamps). Thus, the ""194 patent teaches a device that incorporates three distinct elements: the clamping members, the semicircular member, and the resilient sponge-like block member. While such a device can add more stability when a ladder is used in conjunction with a planar or generally cylindrical surface due to the increased friction between the sponge-like block and the surface, the clamping means preclude the device from being conveniently removed when not required, because a tool is required to release the hose clamps. Often in a work environment, or even at home, several ladders of different sizes are available. It would be desirable to provide a gripping device that can be quickly removed from one ladder and attached to a different ladder so that a single such device could be used with a number of different ladders.
U.S. Pat. No. 1,994,369 describes a generally V-shaped bar that is permanently affixed to the stiles of a ladder near the upper rungs to provide an improve support when the ladder is rested against a pole or other generally cylindrical/round surface. U.S. Pat. No. 3,407,900 describes a flexible strap that is permanently affixed in the same location. Again, while both devices provide more positive engagement and enhanced friction between the upper end of a ladder and a generally cylindrical surface, such devices cannot be readily removed from one ladder to be used with a different ladder, and if attached to the stiles of the ladder, can be cumbersome.
U.S. Pat. Nos. 2,925,877 and 3,828,889 describe devices incorporating a flexible strap that is affixed to an end cap at each end of the strap. The end caps are sized to fit over the tops of the ladder stiles. While such devices can be readily removed from one ladder and placed onto another ladder, due to its design, the strap must be positioned over the end caps of the stiles. Thus, the strap can only be located at the extreme upper end of the ladder. There will be instances in which the optimum location for an accessory that provides improved support when a ladder must be leaned against a generally cylindrical surface will not be at the extreme upper portion of the ladder, but in a position that is somewhat lower.
In 1991, an internal safety committee from an employer requested that OSHA indicate how a ladder should be safely used when rested against a column. OSHA responded by noting that OSHA requires the base of the ladder to be secured if used on a slippery concrete surface (29 CFR 1926.1053(b)(7)), and that stiles at the top of the ladder must be supported equally (29 CFR 1926.1053(b)(10)). As an added precaution, OSHA suggested that body belt/harness systems should be rigged to lifelines attached to the columns, or that means be provided to secure the top of the ladder in place by the use of a wide fork-like attachment at the top of the ladder that would overlap the sides of the column to prevent the ladder from sliding off the column. Notably, OSHA did not suggest the use of any of the prior art devices discussed above, possibly indicating that these prior art devices have not been widely accepted in the marketplace and are not believed by OSHA to provide adequate assurances of safety.
Therefore it would be desirable to develop a device that can enhance the safety of ladders when used with either a planar or a generally cylindrical surface. To become adopted in the marketplace, such a device should be simple to use, easy to remove from one ladder for use on a different ladder, of low cost, and should be readily positionable at any of a plurality of rungs near the upper portion of a ladder to allow greater flexibility in safely positioning the ladder so that it does not slip on a supporting surface, whether the surface is flat or rounded.
In accord with the present invention, a gripping device attachable to a ladder rung for the purpose of stabilizing a ladder is defined. The gripping device includes a generally elongate elastomeric member having at least one slot formed in a front portion thereof. The slot is of a size and shape generally corresponding to that of a rung of a ladder with which the gripping device will be used. The elastomeric properties of the generally elongate elastomeric member cause it to grip a ladder rung with a force sufficient to secure the generally elongate elastomeric member to the rung.
A back surface of the generally elongate member is adapted to provide an enhanced coefficient of friction to increase a frictional force between a structure and an upper portion of the ladder, such that the frictional force stabilizes the ladder. The increased frictional force ensures that it will be less likely the upper portion of the ladder will move relative to the structure supporting the upper portion of the ladder. In one embodiment, the back surface of the elastomeric member includes a plurality of texture elements that further increase the coefficient of friction between the back surface and any surface against which the gripping device and ladder are rested. These texture elements preferably include at least one of a spaced-apart array of spikes, a spaced-apart array of bristles, and outwardly extending ribs. Also preferably, the back surface is concave, such that the gripping device can more readily conform around a generally cylindrical surface.
Preferably, the generally elongate elastomeric member is fabricated as an integral unit from a plastic material. In one embodiment, an internal surface of the slot includes a plurality of texture elements that increase a coefficient of friction between the generally elongate elastomeric member and a ladder rung. These texture elements include at least one of outwardly extending ribs, and bristles.
In another embodiment, a first slot formed in the elongate member grips a rung adjacent to a first stile of the ladder, and a second slot grips the rung adjacent to a second stile of the ladder. The mass of the generally elongate elastomeric member is reduced by including a void space within its interior. One embodiment includes a plurality of voids disposed on the top and bottom surfaces of the generally elongate elastomeric member. In another embodiment, the void space comprises one or more cavities that extend longitudinally through the generally elongate elastomeric member.
Because the cross-sectional shape and area of ladder rungs can vary from one ladder style to the next, the size and shape of the slot in the elongate member is adapted to fit different types of rungs. A cross-sectional shape of the slot includes at least one of a triangle, a circle, a xe2x80x9cDxe2x80x9d shape, and a square.
In one form of the invention, at each end, either the upper or the lower gripping tang of the slot is fabricated as a flexible strap having a plurality of orifices formed in it, and the other of the upper or the lower gripping tang is fabricated as a flexible strap having a knob of a size and shape generally to provide an interference fit through any of the plurality of orifices. The knob on the flexible strap at each end of the elongate member is oriented such that when a ladder rung is inserted into the slot, the flexible strap with the knob engages the flexible strap with the plurality of holes, at both ends, to secure the ladder rung within the slot.